1. Field
The present invention is related to systems and methods for communicating information over a computer network. More specifically, the present invention relates to systems and methods for switching between communication sessions.
2. Description of the Related Art
The number of people using computers to engage in data communication over public and private networks continues to increase dramatically. This increase in network usage is being fueled at least in part by the growing availability of content-rich multimedia data on the Internet and the World Wide Web. Such data is now accessible over the Internet on many types of channels, each having particular advantages. While switching from one channel type to another may result in greater efficiency, existing techniques for such switching cause intolerable disturbances and interruptions in the user's experience as the data are rendered.
The most common type of data channel is a unicast channel. Over a unicast channel, data packets are sent from one computer on the network to another computer on the network. The sending computer includes in each data packet addressing information which identifies the receiving computer. Unicast communication works adequately in many cases, but is not well suited to support current and emerging multimedia applications in which the same large body of data must be transmitted to large numbers of computers.
Another type of channel is a multicast channel. Using a multicast channel, a single data packet can be sent to a group of computers, known as a multicast group, connected to the network. A networked computer can become a member of a multicast group by joining the multicast group, and can relinquish membership by leaving the multicast group. Only computers which are members of the multicast group receive the data transmitted over the multicast channel.
Multicast's efficient use of network resources is particularly advantageous in wide-area multimedia broadcast applications which may involve thousands or even millions of receiving computers. Much efficiency can be gained when a computer receiving a unicast transmission switches to a multicast transmission of the same data.
For various reasons, it is advantageous to begin sending multimedia data via unicast and then switching to multicast. However, with existing techniques, switching from a unicast session to a multicast session is anything but smooth and certainly not transparent to the computer user. This problem results from the loss of data associated with the switch. In most cases, the unicast session utilizes most of the available bandwidth to transmit the unicast data, thus, the bandwidth will be insufficient to handle the additional multicast data (the bandwidth requirement will be roughly twice as high). Therefore, the existing technique of transmitting simultaneous, overlapping unicast and multicast data often results in lost data.
Another existing technique is to stop receiving unicast data and to request and begin receiving multicast data. However, if the unicast session shuts down prior to receiving the multicast data, the time difference between these two operations again results in lost data.
When data are lost in switching from a unicast session to a multicast session, users will experience an unpleasant interruption in the rendering of any media data because of the loss of data associated with the switch. What is needed is a system and method that can provide the computer user with a transparent, seamless, smooth switch from receiving data over a unicast channel to receiving data over a multicast channel.